[ End User Feature ] challenges faced during the procurement and construction of a line pipe project in Oman , as well as the best practices that were implemented to overcome these challenges . Despite the obstacles that arose , the project was completed ahead of schedule , thanks to these practices . This allowed for early installation and commissioning of the pipeline , which was a significant achievement given the difficulties encountered during the project .
Procurement challenges This project required a material that could withstand the corrosive process conditions for a design life of 25 years . While several options were considered , such as carbon steel and carbon steel plus inhibition , these were deemed unacceptable due to maintenance and operational intervention requirements . DSS was chosen for its durability and minimal maintenance requirements . Large diameter and high wall thickness were selected to meet design parameters . However , large-size DSS line pipe procurement posed significant challenges as pipe manufacturers were limited . Three pipe mills participated in the bid , and each proposed different raw material forms and welding methods . As raw material in coil form posed severe challenges in pipe forming and welding for the line pipe size with 24 ” OD and 14.5 and 15.55mm WT , plate form was recommended . However , only a few mills offered raw materials in the plate form in compliance with the project ’ s technical requirements .
Line pipe manufacturing With limited pipe mill participation in the bid , the technical bid evaluations from three different pipe mills were scrutinised for their capabilities , past experiences , and compliance with the stringent technical requirements . All requirements were discussed and elaborated with the chosen pipe mill to ensure compliance without any ambiguity at the ordering stage . The manufacturing procedure , Inspection Test Plan ( ITP ), welding and non-destructive ( NDT ) procedures , and other relevant quality method statements were thoroughly reviewed . A pre-inspection meeting at the mill verified the system and methodology for the new manufacturing process of 24 ” pipe through plate forming , welding , and offline heat treatment and 16 ” & 8 ” pipe through coil forming , welding and online heat treatment .
Fabrication method & welding technique To manufacture the 24 ” DSS line pipe , plates were examined for laminations using ultrasonic testing and joined prior to forming using submerged arc welding . Longitudinal seams were designed with a double-sided full penetration joint configuration . The long seam of the pipe was welded with filler metal in all passes , using plasma arc welding ( PAW ), submerged arc welding ( SAW ), and gas tungsten arc welding ( GTAW ). The welded pipes were subsequently solution annealed , meeting NORSOK conditions in an offline heat treatment furnace . Challenges encountered during manufacturing included modifying weld metal chemistry to ensure a minimum of 0.14 % nitrogen and a minimum Cr and Ni content of the base material . CVN energy values were improved through different trials during the MPQT qualification . The heat treatment furnace was validated during MPQT qualification , complying with NORSOK requirements . Welding repair procedures were also qualified , meeting original weld requirements , and weldability tests were conducted following construction welding variables and testing the weldment in the as-welded condition , meeting ISO 17781 and project specifications . The success of any project hinges on adopting best practices in the construction phases , and welding is no exception . To achieve higher pitting resistance at the root ( which is exposed to the process conditions ) in the as-welded condition , weld metal was designed with SDSS filler wire to meet the pitting resistance of the base material ( which was solution annealed ). In the field , it is a harsh environment where the mercury rises to 55 ° C , and the resultant ambient metal temperature of the pipe to 60 ° C poses high challenges to meet the inter-pass temperature requirement for welding DSS . Critical welding parameters ( interpass temperature and heat input ) were qualified under the worst conditions during procedure qualifications to avoid construction difficulties . Welders and welding operators were also systematically trained before deployment . Another critical factor is the oxygen content , which must remain below 500ppm , or the value demonstrated in the welding qualification procedure to avoid oxidation . This was achieved by introducing dual inlet and high flow rates , as well as a double sealant purge dam with a dual inlet to maintain
Figure 2 . SAW welding for doubling joints in the yard to increase productivity .
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